The present invention relates to a technology for suppressing degradation of a display quality when a plurality of data lines is driven in group.
For display panels that perform display by the electro-optical change of an electro-optical material, e.g., liquid crystal display panels using a liquid crystal can be classified into several categories based on a driving scheme. However, for an active matrix driving a pixel electrode with a three terminal type switching device, the following arrangement is typically used. Specifically, in this type of liquid crystal panel, a liquid crystal is interposed between a pair of substrates, and a plurality of scanning lines 112 are arranged to intersect a plurality of data lines 114 on one substrate, as shown in FIG. 7. In addition, thin film transistors 116 (hereinafter, referred to as TFT) and pixel electrodes 118 are arranged on one substrate at the corresponding respective intersections of the scanning lines 112 and the data lines 114. Further, transparent counter electrodes 108 (common electrodes) maintained at a constant voltage LCcom are arranged to face the pixel electrode 118 on the other substrate, and TN liquid crystals 105 are interposed between two electrodes. For this reason, a liquid crystal capacitor comprising the pixel electrode 118, the counter electrode 108 and the liquid crystal 105 is provided for each pixel.
In addition, on each facing surface of both substrates, a rubbing processed alignment film (not shown) is arranged such that a long axis direction of the liquid crystal molecule is consecutively tilted, for example, about 90 degrees between both substrates, while a polarizer is arranged on each of opposition side of both substrates according to the alignment direction.
In addition, to prevent the charge leakage in the liquid crystal capacitor, a storage capacitor 119 is arranged for each pixel. One end of the storage capacitor 119 is connected to a pixel electrode 118 (a drain of TFT 116), while the other end is commonly grounded to potential Gnd throughout entire pixels. According to the present embodiment, the other end of the storage capacitor 119 is grounded to potential Gnd, it may be applied to a predetermined potential (e.g., voltage LCcom, a high level power supply voltage of the driving circuit, or a low level power supply voltage of the driving circuit, etc.).
For convenience, assuming that a total number of scanning lines 112 is ‘m’, a total number of data lines 114 is ‘6n’, (where, m and n are integers, respectively), pixels are arranged in a matrix of m row×6n column corresponding to each intersection located between the scanning lines 112 and the data lines 114.
A light transmitting between the pixel electrode 118 and the counter electrode 108 is refracted about 90 degrees along with the tilt of the liquid crystal when an effective voltage of the liquid crystal capacitor is zero, while as the effective voltage grows larger, the liquid crystal molecule is tilted toward the electric field. Therefore, its optical activity is lost. For this reason, in the transmission type, for example, in case that a polarizer whose polarizing axis is perpendicular to each other to match the alignment direction is arranged at each incident side the bottom side (in a normally white mode), when the effective voltage of the liquid crystal capacitor is zero, light is transmitted to perform a white display (large transmittance), while as the effective voltage becomes larger, the amount of transmitted light is reduced to perform a black display (smallest transmittance). Therefore, when the TFT 116 is turned on by selecting each one of the scanning lines 112, the image signal of the voltage corresponding to a gray scale level (or brightness) of the pixel is applied to the pixel electrode 118 via the data line 114, such that the effective voltage of the liquid crystal capacitor can be controlled for each pixel. Further, the predetermined display is enabled based on this control.
Here, although the liquid crystal panel can be used as a light valve such as a projector. However, the projector does not have any function to make images in its own, and thus it receives an image signal from the upper level apparatus such as a PC or a television tuner. The image signal is provided in a manner of horizontally and vertically scanning images arranged in a matrix. Therefore, for the liquid crystal panel used for the projector, it is appropriate to meet this specification. Accordingly, for the liquid crystal panel used for the projector, a method of point-sequential driving is employed as a driving scheme to provide the image signal to the data line 114. In the method of point-sequential driving, an image signal transformed from a video signal to be adapted to the liquid crystal driving is sampled to the data line for one data line 114, during a period one scanning line 112 is selected (one horizontal effective scanning period).
In addition, recently, there is a strong need for a high definition such as Hi-Vision. The high definition can be accomplished by increasing the number of scanning lines 112 and the data lines 114. However, as the number of scanning lines 112 increases, the horizontal scanning period is shortened. Moreover, with a point-sequential method, as the number of data lines 114 increases, the sampling time to the data line 114 is also reduced. Likewise, in case of the high definition, with the point-sequential method, the sampling time to the data line 114 is not sufficiently secured for the image signal, such that a phase expansion driving method as shown in FIG. 8 is employed. In the phase expansion driving method, while the arrangement in the display region 110a are not changed from that of FIG. 7, the data lines 114 are blocked for every predetermined number (e.g., 6) and the image signal is distributed into 6 channels corresponding to the number of the data lines 114 included in one block. In addition, the image signal is expanded 6 times longer in the time axis, and thus provided to the image signal line 171 as image signals Vid1 to Vid6.
Further, to one end of the data line 114 arranged leftmost among 6 data lines 114 belonging to the i-th row block (where, i is 1, 2, . . . , n) counting from the left side in FIG. 8, a drain of an N channel TFT 151 is connected as a sampling switch, while a source thereof is connected to the image signal 171 to which the image signal Vid1 is provided. Likewise, to one end of the data line 114 arranged at second, third, . . . , sixth row counting from the left side of the corresponding block, drains of the corresponding TFTs 151 are connected, while sources thereof are connected to the image signal line 171 to which the image signals Vid2, Vid3, . . . , Vid6 are provided.
In addition, in FIG. 8, a scanning line driving circuit 130 outputs scanning signals G1, G2, G3, . . . , and Gm, which sequentially and exclusively come to be an H level, by means of a clock signal CLY or a start pulse DY within one vertical effective scanning period. Further, a shift register 140 outputs sampling signals S1, S2, S3, . . . , and Sn, which sequentially and exclusively come to be an H level, by means of a clock signal CLX or a start pulse DX within one horizontal effective scanning period.
In the phase expansion driving, each block is selectively one by one within the one horizontal effective scanning period, by sampling signals S1, S2, S3, . . . , and Sn. Here, for example, when an i-th row block is selected, i.e., a sampling signal Si comes to be an H level, 6 TFTs 151 where drains are connected to the data lines 114 belonging to the related block are simultaneously turned on. Therefore, for each of the first, second, third, . . . , and sixth row data lines 114 belonging to the related block, each of the image signals Vid1, Vid2, Vid3, . . . , and Vid6 is sampled.
In the phase expansion driving, compared to the arrangement where the image signal is sampled by selecting the data lines 114 one by one, the time required in sampling can be made 6 times longer. Therefore, the phase expansion driving can be used to achieve high definition, as described above. Furthermore, while the number of data lines contained in one block is assumed to be 6, this is just illustrative, and thus the present invention is not limited hereto.
However, in the phase expansion driving, since the plurality of data lines 114 are grouped and driven in blocks, a so-called block irregularity representing that brightness of the pixels are different for each block is produced. Regarding this, the present invention proposes a technology for make the block irregularity unnoticeable by making correction signals based on the difference between the image signals of the respective channels and the reference signal to add the correction signal to the respective channels.